Sahih Bukhari Volume 001, Book 002, Hadith Number 023.
Narated By 'Abdullah (bin 'Umar) : Once Allah's Apostle passed by an Ansari (man) who was admonishing to his brother regarding Haya'. On that Allah's Apostle said, "Leave him as Haya' is a part of faith." (See Hadith No. 8)